A process by which pigment with pearlescent effect is prepared using sheet-like materials as a substrate and single-layer or multilayer oxides as a coating has been adopted for several decades, is highly mature, and has a large amount of patents. A process that forced hydrolysis coating is performed through water-soluble metal salt at a preset PH value is a commonly used technique, since the water-soluble metal salt is acidic generally, and alkali must be added during continuous addition of the water-soluble metal salt to balance the PH value, otherwise the hydrolysis cannot be performed continuously. Metal hydroxides, such as NaOH and KOH, are mainly used to neutralize acid and alkali currently. Aqueous ammonia (NH3.H2O), sodium carbonate (Na2CO3) or the like can also be used to control the PH value to perform hydrolysis coating. The abovementioned alkalis all can dissolve in water, and are generally made into a water solution before added to a reaction kettle in production. Even though added in a solid form, the water-soluble alkali is dissolved to form a solution after entering the reaction kettle, and also provides required hydroxyl (OH−) to neutralize the acid (H+) to achieve a purpose of maintaining a stable PH value. The process has the following defects: when the alkali enters the reaction kettle, local overhigh alkali concentration occurs unavoidably, and in addition to neutralizing the acid, the local overhigh-concentration alkali (OH−) may further combine with coating metal ions (such as Ti4+, TiO2+, Fe3+ and Sn4+) to produce metal hydroxide (or hydrated metal oxide) sediment, and does not completely coat the sheet-like substrate, thus forming free substances. Since the free substances have high absorption capability due to a small size (nanoscale generally) and a large specific surface area, the hydrolysis coating compete between the free particles and the sheet-like substrate subsequently. Once being formed, the free particles are removed only by subsequent steps of filtering, washing, gas flow classifying and the like, since the free particles can lower colourity of the pearlescent pigment and cause various problems during application. Even though the free particles can be reduced by stirring and a strict control of a feeding speed, the free particles cannot be eliminated completely by the foregoing process.